You would need to use an AudioBox iOne or iTwo with the MFi interface that would allow you to get audio into your iOS device and out to your sound board using the (Made For iOS) interface. Since your Camera connects to your phone via Wi-Fi and Bluetooth, all your audio would go over USB through the Lightning Cable.
The Audio input on an iOS device is either the onboard Mic or something connected to the USB interface inside the Lightning connector (ie MFi or USB Audio device connected via the Apple Camera Connection Kit).
We have not tested this, and we would suggest finding someone or a PreSonus dealer who has an MFi USB Audio Interface and try it out to be sure.